Service providers provide telephony service to their customers using systems known generically as either circuit or packet switched systems. Circuit switched systems send data signals continuously over telephone lines to provide both Internet access and conventional analog telephony. Packet switched systems, such as the Internet, serve as a transport medium for carrying voice and data in packet form. One of the main differences between these technologies is that the circuit switched systems have a continuous circuit whereas packet switch systems transmit bursts of packets in a discontinuous manner.
When two modems (e.g., a user modem and a service provider modem) connect via a circuit switched system, such as the public switched telephone network (“PSTN”), they exchange a sequence of signals to determine a type of modulation that both modems support and that will be used for the connection between them.
Similarly, when two modems connect via a packet switched network with MoIP endpoints, they exchange signals in order to establish a connection, which can consist of one or two physical layer connections between the two modems. A one-layer connection over a packet network consists of a connection directly between the two modems and is referred to as a voice-band data (“VBD”) mode connection. A two physical layer connection consists of a connection between one packet network MoIP endpoint and one modem and a connection between the other packet network MoIP and the other modem, and is referred to as a modem relay (“MR”) mode connection. In the latter case, there are essentially four modems involved in the end-to-end connection between the two modems: each MoIP endpoint and its adjacent modem.
Service providers that are sensitive to the characteristics of modem connections between modems from different manufacturers may object to the fact that there may now be four modems involved in a connection when conventionally there were only two involved in a PSTN connection. In addition, with a PSTN connection, a service provider had control of the physical layer connections between modems. For example, a service provider could specify a type of modulation to be used. However, in the MR mode of a packet network connection, service providers have no control over the two “inner” modems of the MoIP network endpoints, which may not even be visible to them. Client users may have similar concerns.
In contrast, other modem users may desire to send data in the MR mode because of its improved performance and maximized efficiency. Service providers may desire data transfer to be completed in the MR mode, for example.
To address these concerns, service providers may want MoIP packet network endpoints to make only VBD connections to retain a one-layer connection over the packet network, as in traditional circuit switched networks or to make only MR connections. While a VBD mode-only endpoint can readily be constructed by simply not implementing any modulations in MR mode, it is desirable, for maximum interoperability, to have a mechanism negotiated at call setup that would allow for a negotiation between the use of a VBD mode connection or an MR mode connection for a call.